People use the "complete circle" of sonotube for subs, which being a complete circle is strong.

My idea might not be suitable for enclosures likely to have higher internal air pressure, ie to play at higher volumes, to play deeper bass and/ or especailly totally sealed boxes.

To reduce internal standing waves but keep construction simple, the back and/ or sides of boxes be formed from a section of sonotube, ie maybe a quarter or a half of the circle.

An advantage of sonotube is that it’s light, so stored energy will be low. What I don’t know is how rigid it’d be. If two layers were glued to each other, it’d be a lot stiffer, and still very light.

As you go up the scale of sonotube diameters, they become a little thicker. As a guide, the local brand here in 400 mm (16”) diameter is 6.4 mm (0.25”) thick.

If the enclosure were to be braced back to front, for strength you’d probably want to face the curve “convex in”, etc

I think it might be rigid enough for small medium volume enclosures: bookshelfs, “monitors”, mids, full fangers etc. Any knowledge of the stiffness of curved cardboard; for which applications the rigidity would be enough?

Maybe it could be made stiffer by eg 'painting' with a two part epoxy . .

Practical problems with using sections of cardboard rolls (incl concrete formers) is how to protect and finish (hide) the cut edges and how to keep its original shape. Once cut, it springs apart. So now you're almost making a frame or channel to hold the tube section, and the edges have no real strength to fasten to.
But it's worth trying for a different look.

Consider using a section of large PVC sewer or plumbing pipe. Does the arc at the point you intend really need to have a 16" diameter? The PVC might work for the back, but probably not for the sides.

The way arced or arched cabinets are usually made is by sawing a groove into the plywood or MDF say every 0.5" to 0.75". This will allows the MDF to bend into the grooves. This was recently discussed here; I will see if i can find the link -

One method of using tubes is a straight cut to open it up and then
inserting a flat baffle into the opened out tube. Only suits multiple
small drivers though but can look good. The baffle usually just
needs a V slot in its sides to locate the tube edges.

A guy I used to know owned a wood products manufacturing company. Back in the 1960s and 1970s, they (also) made things like drum 'shells', and I think maybe cello bodies, and other wooden things with curved shapes.

The way they did it, back then, was basically to 'form their own plywood', in whatever shape they wanted. They used thin wood plies (which they had earlier peeled off of hardwood logs, themselves, with a veneer mill), applied special glue, placed the plies together and used something to hold them in the precise shape needed, and then cured the glue.

That was the one 'neat trick' that made me remember it: The glue they used cured "instantly", when exposed to strong-enough radio waves of the proper frequency! (At one point, apparently, the FCC barged in and told them that they had been interfering with ship-to-shore communications near Cape Cod, which is a long way from SW Indiana. After that, they did it all inside of a completely-screen-shielded area.)